TABLE OF CONTENTS Single-phase induction motors are widely used in small power applications where the provision of polyphase power is impossible (as in domestic applications) or uneconomical. Single-phase induction motors share most advantages of polyphase motors: they are rugged and economical to build. Typically, single-phase motors are larger and less efflcient than comparable polyphase motors and require special means for starting. They are therefore somewhat more expensive. In some cases, the starting mechanism involves a switch and this is an extra point of vulnerability which can lead to lower reliability.
This section includes the expressions required to analyze the basic operation of single-phase induction motors. It starts with the running operation of the motor on a single winding, using much of the notation developed for polyphase motors. It is then extended to include a second, auxiliary winding to show how these motors can be started.
Figure 4.32 shows a "cartoon-style" drawing of a single-phase motor. The "main" winding is contained in slots in the stator structure. Shown also is an "auxiliary" winding, usually situated in quadrature with the main winding, leading it by 90 electrical degrees. The auxiliary winding is, generally, not identical to the main winding.
Once a single-phase machine is turning, it will develop torque. In fact, many applications of single-phase motors use a starting mechanism which is removed once the motor is started, so that it actually runs as a true single-phase machine.
